Free and total cholesterol has been quantitated in fractionated thoracic duct lymph, HDL subfractions HDL2a, HDL2b, and HDL3 using the micromethod developed in our laboratory. Cholesterol analyzer sensitivity has been improved so that as little as 1 mg/dl of free cholesterol can be quantitated enzymically. The normal ranges for C-II and LpB have been established by radial immunodiffusion. Normal ranges for A-I and A-II apolipoproteins have been remeasured. A-I immunoquantitation has been studied by rate nephelometry for protein-protein interations.